1. Technical Field
The invention relates to a universal serial bus (USB) port attached to a host computer, particularly to a USB port with uninterruptible power to provide USB device charging functionality when the host computer is in a standby mode.
2. Related Art
For many electronic devices such as personal computers (PCs), cellular phones and digital cameras, universal series bus (USB) has become a standard connection port. Unlike the older connection standards RS-232 or Parallel port, USB connectors also supply electric power, so many devices connected by USB do not need a power source of their own. For some portable electronic devices with built-in batteries, a USB port may charge the battery and make data communication simultaneously when an electronic device is connected to a computer via the USB port. Besides, A USB port also can be used to only serve as a power outlet without data communication.
Modern computers must adopt the Advanced Configuration and Power Interface (ACPI) specification for power management. In the ACPI, there are six power states: S0, S1, S2, S3, S4, and S5, in which SO is a working state and S3-S5 may be deemed as of a power down state. Normally, a computer will turn off power output of USB ports thereof when the computer is switched into the power down state. In more detail, there is no power provided to USB port when in S4 and S5, and there is possibly limited power when in S3, very low current which is not enough to be used for charging. In other words, USB ports of a computer have no or almost no power output when the computer is in the power down state. However, some users may still require the power output of USB ports when they switch their computers into the power down state, for example, using USB ports to charge batteries of portable apparatuses such as mobile phones, MP3 players, tablet PCs, etc.
To satisfy this requirement, some computers adopt modified design of USB power. In such a computer 7, as shown in FIG. 1, a charging controller 722 is disposed in a motherboard 72 to control a specific USB port 723. The charging controller 722 and the CPU are in the same motherboard 72. The CPU 721 outputs a power state signal to the charging controller 722 to indicate a power state of the system. On the other hand, the charging controller 722 acquires power from the power supply 71 of the computer 7. In this figure, the broken line between the power supply 71 and charging controller 722 stands for a power line. As a result, the charging controller 722 can keep supplying power to the specific USB port 723 when the computer has been switched into the power down mode because the charging controller 722 is aware of the power state. Thus, users may utilize the specific USB port 723 to charge a battery even when the computer 7 has been into the power down state. This function can be achieved only by a specialized motherboard 72. However, a specialized motherboard is much more expensive than a standard one in manufacturing cost.
However, not all computers have such a special design. A normally standard motherboard without the specific USB port cannot charge a battery any longer when the computer has been in the power down state. This is a problem to be solved. Some computer system manufactures who prefer to adopt standard motherboards must meet this problem if they don't or can't adopt the specialized motherboard. These manufactures usually use an input/output (I/O) module, such as a card reader, to connect a standard motherboard for increasing I/O ability. Thus, an I/O module with a power-uninterruptible USB port will be an economic and effective solution for these manufactures. Unfortunately, such an I/O module has never appeared in the market.